Dental root canal sealing compositions are frequently applied into the root canal through a canal of a needle. Due to the small dimensions of the needle canal, the compositions are required to have a low viscosity. Alternatively, dental root canal sealing compositions are applied by using lentulos or gutta percha tips. Accordingly, the viscosity must be low so that thin films may be formed. Independent from the application technique, the viscosity of the material must be low enough so that the composition may enter into dentin canals in the root canal.
The application of dental root canal sealing compositions is checked by using X-ray procedures. Due to the requirement for radioopacity, the compositions are required to contain a substantial amount of a radioopaque filler.
Dental root canal sealing compositions are known from WO 02/13767 disclosing in the application examples a two-component paste/paste system. The two-component paste/paste system is based on addition polymerisation of equimolar amounts of low-molecular diamines and low-molecular diacrylates optionally in the presence of a reactive diluent for ajusting the viscosity of the composition.
Recently, root canal sealing materials composed of primary monoamines and/or disecondary diamines and diepoxides (U.S. Pat. No. 5,624,976), diacrylates (WO 02/13767) and bisacrylamides (WO 02/13768) were disclosed. These materials exhibit some advantageous properties such as relative long working time due to the slow addition polymerisation, high radio opacity, low volumetric shrinkage, low solubility and a tight sealing ability (Int. Endod. J. January 2003; 36 (1):54-63; Int. Endod. J. September 1999; 32 (5): 415-8; Aust. Endod. J. April 2001; 27 (1): 33-5; J. Endod. March 1999; 25 (3): 172-7)).
However, the presence of low molecular amines in the dental root canal sealing composition leads to severe drawbacks. Cytotoxic effects are frequently observed due to leaching of such amines from the root canal. Moreover, the cured compositions of WO 02/13767 show a considerable solubility whereby the cytotoxicity problem is aggravated and further application problems are created. Finally, the high vapor pressure of low molecular amines and the high penetration rate through plastic packaging render the compositions of WO 02/13767 problematic for industrial application. (Endod. Dent. Traumatol. August 1998; 14 (4): 182-5; Endod. Dent. Traumatol. December 2000; 16 (6): 287-90; J. Endod. August 2000; 26 (8): 462-5; J. Endod. April 2000; 26 (4): 228-9)).
Polyaminoesters specifically disclosed in WO 02/13767 are highly viscous and require the use of a substantial amount of reactive diluent in order to decrease the viscosity. However, reactive diluents cannot be polymerised by addition polymerisation, but require the presence of a polymerisation initiator.
US2002/0143108 discloses polymeriable macromonomers obtainable by a two-step reaction wherein in a first step a diepoxide is reacted with a disecondary diamine for providing an intermediate prepolymer which is reacted in a second step with 2,3-epoxypropyl-(meth)acrylate. According to the corresponding Referential Example 5, the intermediate prepolymer is not isolated. Accordingly, US2002/0143108 cannot disclose the intermediate prepolymer. Moreover, US2002/0143108 does not disclose an intermediate prepolymer suitable for providing an amino terminated prepolymer having a viscosity at 23° C. of less than 100 Pas.
It is the problem of the present invention to provide a dental root canal sealing composition having a low viscosity, low cytotoxicity, and low solubility while having excellent mechanical properties such as low shrinkage and flexibility and which do not give rise to handling problems during manufacture and application.